Stabilization of mixtures of polyamide, epoxy resin solutions with formic acid



United States Patent STABILIZATION OF MIXTURES OF POLYAMIDE, EPOXY RESIN SOLUTIONS WITH FORMIC ACID David Glaser, St. Paul, Minn, assignor to General Mills, Inc., a corporation of Delaware No Drawing. Application February 23, 1954 Serial No. 412,095

3 Claims. (Cl. 260-18) The present invention relates to stabilizers for mixtures of polyamide resins and epoxy resins. As disclosed in the patent application of Harold Wittcofi and Malcolm Renfrew, Ser. No. 276,054, filed March 11, 1952, entitled Thermosetting Resinous Compositions, now Patent No. 2,705,223, polyamide resins derived from polymeric fat acids may be used to cure epoxy resins. These compositions may be prepared by mixing solutions of the respective resins and applying the mixed solution for the particular application desired. These mixed solutions, however, cure very rapidly and accordingly, it has been necessary heretofore to maintain the two solutions separate until immediately prior to use. In other words, the mixed solution of resins has a relatively short life before gelation occurs.

It has now been discovered that it is possible to produce mixed polyamide resin-epoxy resin compositions which are stable for extended periods of time without danger of curing or gelation. This stabilization of the mixed resin composition is obtained by the inclusion of formic acid in the mixture. These compositions may be caused to cure rapidly after application to produce hard infusible insoluble compositions resistant to water and various chemical materials.

It is, therefore, an object of the present invention to provide a process of stabilizing mixtures of polyamide resins and epoxy resins to prevent the premature gelation or curing of the same. It is another object of the present invention to provide stabilized compositions comprising mixtures of polyamide resins and epoxy resins.

The present invention is applicable to epoxy resins in general. These epoxy resins are complex polymeric reaction products of polyhydric phenols with polyfunctional halohydrins such as cpichlorhydrin and glycerolv dichlorhydrin. Uusally the difunctional chlorhydrin is used in proportions in excess of that equivalent to the polyhydric phenol and less than that which is twice the equivalent amount. The reaction is carried out in the presence of caustic alkali which is usually employed in at least the quantity necessary to combine with the halogen liberated from the halohydrin, and usually is employed in excess. The products obtained may contain terminal epoxy groups or terminal epoxy groups and terminal primary hydroxyl groups. In the complex reaction mixture the terminal epoxy groups are generally in excess of the terminal primary hydroxyl groups. Typical polyhydric phenols include resorcinol, and various bisphenols resulting from the condensation of phenol with aldehydes and ketones such as formaldehyde, acetaldehyde, acetone, methyl ethyl ketone, and the like. Resins of this type are disclosed in Greenlee Patent 2,585,115 and theseresins are useful in the present invention.

The molecular weight of the epoxy resins may be controlled by the relative proportions of the reactants, as Well as by the extent to which the reaction is carried on. The present invention involving the curing of these epoxy resins may be applied to all epoxy resins. The molecular weight of the resin is not critical since both very low molecular weight resins, as well as very high molecular weight resins, can be cured by this method. The properties of the cured resin compositions may, of course, vary with the molecular weight of the epoxy resin employed, as Well as the nature and molecular weight of the polyamide employed.

The polyamide compositions which may be used for curing the epoxy resins are, in general, those derived from polymeric fat acids and polyalkylene polyamines. Resins of this general type are disclosed in Cowan et al. Patent 2,450,940. Typical of these polyamides are those made with polymeric fat acids and diethylene triamine. These polyamides have a relatively high amine number due to the free amine groups. The amine number is defined as the number of milligrams of potassium hydroxide equivalent to the free amine groups present in one gram of the resin. In general, resins having amine numbers within a range of 50 250 are preferred for the present purposes.

The polymeric fat acids employed in preparing the polyamides are those resulting from the polymerization of drying or semi-drying oils, or the free acids or simple aliphatic alcohol esters of such acids. Suitable drying or semi-drying oils include soybean, linseed, tung, perilla, oiticica, cottonseed, corn, tall, sunflower, safiiower, dehydrated castor oil and the like. In the polymerization process for the prepartion of the polymeric fat acids, the fatty acids with sufiicient double bond functionality combine, for the most part probably by a Diels-Alder mechanism, to provide a mixture of dibasic and higher polymeric acids. The acids with insufiicient functionality to react remain as monomers and may be wholly or partially removed, for example by distillation. The residue after distillation consists of the desired polymeric acids and this mixture is used for the preparation of the polyamide resin. In place of this method of polymerization, any other method of polymerization may be employed, whether the resultant polymer possesses residual unsaturation or not. The term polymeric fat acids as used herein is intended to include the polymerized mixture of acids obtained, which mixture usually contains a predominant portion of dimeric acids, a smaller quantity of trimeric and higher polymeric acids, and some residual monomer.

These polymeric fat acids may be reacted with a variety of polyalkylene polyamines, such as diethylene triamine, triethylene tetramine, dipropylene triamine, 3,3'-iminobispropylamine, etc. The amidification reaction may be carried out under the usual conditions employed for this purpose. Polyamides of this type generally have molecular weights varying from 1,000 to 10,000 and are resistant to the corrosive action of water, alkali, acids, oils,

, greases and organic solvents. The melting points vary,

depending upon the reactants and the reaction conditions. A preferred group of these low melting polyamides are derived from polymeric fat acids and diethylene triamine and melt at from 40 to 70 C.

There is a wide variation in the relative proportions of the polyamide resin and the epoxy resin which may be employed. The polyamide resin may be considered as the curing agent for the epoxy resin when the polyamide is employed as the minor constituent. At the same time the polyamide may be employed as the major constituent with a minor amount of epoxy resin in which case it may be considered that the epoxy resin serves to cure the polyamide. Thus compositions varying from 10% epoxy resin and of polyamide resin to 90% epoxy resin and 10% polyamide resin have been prepared and have desirable, though varying, properties. For example, when 10% of an epoxy resin is used with 90% of a polyamide resin derived from equimolar portions of diethylene triamine and polymeric fat acids, a

amide is used with 90% of the epoxy resin, 21' hard,.

highly resilient composition results. Between these ex- With the preferred polyamides, that is those derived from diethylene triamine and polymeric fat acids, it is found that the polyamides have an amine number which varies from approximately 80 to approximately 100. A

tremes all other proportions are possible and the prop- 5 quantity of formic acid, approximately 8% y Weight erties vary with the particular composition. The solvent based on the weight of the polyamide, is sufiicient to resistance and mechanical resistanceof all the composineutralize all of the free amine groups and prov de a tions are excellent. Since the epoxy resin may vary in slight excess. With polyamides derived from higher the content of epoxy groups and since the polyamides functional amines such as triethylene tetramine thequanmay vary in number of excess amine groups, it is apl tity of formic acid required for complete neutralization parent that the properties which are obtained depend s n i lly g t rupon the relative proportions of the various functional It Will be found that the viscosity a h -P groups present. In general, the free amine groups should pared solution of the mixed polyamides containing the be present in an amount equivalent to at least one formic acid is appreciably higher than a freshly-prequarier f th epoxy groups Si il l th epoxy l pared solution of the same resins which does not contain groups should be present in a quantity which is equivathe formic acid. The presence of the formic acid aplent to at least one quarter of the free amine groups. pears to increase the initial viscosity Somewhat Th resins may b i d i h f f h i 1 ever, it is found that once the composition stabilized tions. The polyamides are soluble in aromatic hydro- With formic acid is Prepared, that there is felatlvely carbons such as toluene mixed with aliphatic alcohols little Change n Viscosity over extendcd time P such as isopropanol, n-butanol and the like. The epoxy Thus, stabilized compositions will be found to be in an resins are soluble principally in ketone solvents and the llflgelled Condition after even three to foul" h two resins may be separately dissolved and the solutions Whereas the Same Composition Without the formic field mixed to obtain a composition which may be cured. p y gel ill a matter of one to three y The stabilization of the mixed resins is obtained by The formic acid may he P Y in y 0f the forms the inclusion 0f a Smah amount f fgrmi acid in the commercially available. Usually it is available in forms mixed composition. It is believed that the formic acid of 85 to 100% P y f balance of the material being reacts with the free amine groups to form salts which Water- The formic acid y he added y 0 the render the amine groups unavailable for reaction with mixed Solutions and it found that it dissolves and the epoxy Upon application f the mixed forms a homogeneous mixture. The small quantity of position, for example, in the form of film, the formic Water h y mp y the f h held dOeS'IIOt i may vaporize, especially i the case f baked coatin any way interfere with the stabilization of the mixed ings, and thus make the amine groups available for re- Teslhsaction with the epoxy groups. At room temperature, Example 1 curing of the mixture after application is somewhat slow- A Solution of a polyamide resin, d i d f l er than is the case at elevated temperatures encountered meric f t acids and methylene triamine having an mine in baked coatings. However, even at room temperature number f 5 was prepared i a solvent mixtum the air-dried Coatings cure and Produce hard resistant posed of xylene, n-butanol 4:1. The solution contained films I11 ease of baked coatings, the fefmie acid 50% polyamide resin by Weight. A second solution was pp y vapol'iles readily and these Coatings Cure in 40 prepared from an epoxy resin (Epon 1001) in a 1:1 mixapproximately the same period of time required for the ture of methyl isobutyl ketone and xylene, the solution curing of coatings which do not contain the formic acid. ontaining epoxy resin solid by weight. These two The properties obtained from the baked coatings are solutions were mixed in equal volumes. A control approximately the same as are obtained from baked coatsample was taken from this mixture and also a series of ings which do not include the formic acid. The high samples were prepared containing varying amounts of temperature employed for the baking apparently subformic acid. These samples were then stored in sealed stantially completely removes the formic acid. containers and the viscosity noted over a period of time.

The quantity of formic acid employed may be varied The results are indicated in the following table:

Percent Viscosity atter Sample HOOOH Vise.

by wt. T181) 3days 7days 11 days 27 days 53 days 67days Control-- 0 J Gelled i 3.9 T Y-Z 5.1 T U Y-z 6.4 T U-V W 8.2 T T-U U-V 8.7 T T-U my 9.2 s T T-U 10.2 S T U 15.3 M N QR considerably depending upon the particular type of prod- Example 2 not desucd and penod i .stablhzatloli which Is A solution of a polyamide resin derived from polynecesary .Even quanmles. of formlc acid i meric fat acids and triethylene tetramine, having an efiecnve.to i i hfe the mlxture The quanmy amine number of 230 was prepared in a solvent mixture of formlc and 9 may be employed vary i composed of xylene and n-butanol (4:1). The solusuch a Small quanmy aS 25% of tha quanmy requlrFd tion contained 50% polyamide resin by weight. A seeto f f fi the amme groups to h quantity 0nd solution was prepared from an epoxy resin (Epon which Is eqmv.a1em to 100% of the free amme h 70 1001) in a 1:1 mixture of methyl isobutyl ketone and It is also possible to employ an excess of formic acid Xylene, h l ti containing 50% epoxy resin by and above that reqlhfed complete helltrahzatloh weight. These two solutions were mixed in the volumes vof the free amine groups but the excess does not pp indicated in the table below so that the mixed solutions to contribute any advantages and accordingly the use contained approximately the proportions by weight inof an excess is not preferred.

dicated. A control sample was taken of a 50:50 mixture and varying amounts of formic acid were added to the other mixtures. These samples were then stored in sealed containers and the viscosity change noted over a period The effect of formic acid on the stability of mixtures of the polyamide from Example 1 and various epoxy resins was determined in each instance. The polyamide and the epoxy resin were dissolved in the solvents indicated to prepare 50% solutions by weight. These solutions were then mixed in equal volume so that the solutions contained approximately equal quantities of polyamide resin and epoxy resin. The quantities of formic acid based on the weight of the polyamide was then added. The results are indicated in the following table:

Percent Vise. after- Sample Type Epoxy HOOOH Initial by wt. Visc.

1 day 5 days 0 I-J S Gelled 9. 2 M M P 0 E K Gelled 9. 2 .T I Epon 1007.... 0 V Z Gelled Epon 1007-.- 9. 2 Z Z Z In the above tables the percentage of formic is based on the polyamide and the viscosities are Gardner-Holdt.

I hereby claim as my invention:

1. A mixture of an epoxy resinous material containing terminal epoxy groups, and a polyamide having an amine number of at least and being derived from the reaction of polymeric fat acids and a polyalkylene polyamine, the mixture being stabilized against gelation by means of formic acid varying in quantity from 25 to of the quantity equivalent to the free amine groups in the polyamide resin.

2. A stabilized solution of epoxy resinous material containing terminal epoxy groups and being derived by the reaction of a bisphenol with a material selected from the group consisting of glycerol dichlorhydrin and epichlorhydrin, and a polyamide having an amine number of at least 50 and being derived from the reaction of polymeric fat acids and diethylene triamine, the solution being stabilized against gelation by means of a quantity of formic acid equivalent to from 25100% of the free amine groups in the polyamide.

3. A stabilized solution of an epoxy resinous material containing terminal epoxy groups and a polyamide derived from the reaction of polymeric fat acids and a polyalkylene polyamine, the solution being stabilized against gelation by means of a quantity of formic acid approximately equivalent to the free amine groups in the polyamide resin.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A MIXTURE OF AN EPOXY RESINOUS MATERIAL CONTAINING TERMINAL EPOXY GROUPS, AND A POLYAMIDE HAVING AN AMINE NUMBER OF AT LEAST 50 AND BEING DERIVED FROM THE REACTION OF POLYMERIC FAT ACIDS AND A POLYALKYLENE POLYAMINE, THE MIXTURE BEING STABILIZED AGAINST GELATION BY MEANS OF FORMIC ACID VARYING IN QUANTITY FROM 25 TO 100% OF THE QUANTITY EQUIVALENT TO THE FREE AMINE GROUPS IN THE POLYAMIDE RESIN. 